diff --git a/quad_pyblish_module/plugins/maya/publish/validate_arnold_camera_metadata.py b/quad_pyblish_module/plugins/maya/publish/validate_arnold_camera_metadata.py
index 1a503c9..861177e 100644
--- a/quad_pyblish_module/plugins/maya/publish/validate_arnold_camera_metadata.py
+++ b/quad_pyblish_module/plugins/maya/publish/validate_arnold_camera_metadata.py
@@ -126,7 +126,7 @@ def process(self, instance):
         # Add post render mel command to validate metadata
         post_mel_command = 'python("from quad_pyblish_module.plugins.maya.publish.validate_arnold_camera_metadata import ' \
                            'ValidateArnoldCameraMetadata; ValidateArnoldCameraMetadata().process(None)")'
-        post_mel_current_value = lib.get_attribute('defaultRenderGlobals.postMel')
-        if not post_mel_command in post_mel_current_value:
+        post_mel_current_value = lib.get_attribute('defaultRenderGlobals.postMel') or ''
+        if post_mel_command not in post_mel_current_value:
             post_mel_command += '; ' + post_mel_current_value
             lib.set_attribute('postMel', post_mel_command, 'defaultRenderGlobals')